Switching circuit for radio frequency isolation in a portable transceiver

ABSTRACT

Semiconductor switches in portable transceivers switch between outgoing and incoming radio frequency signal paths. The isolation can be limited by the capacitive coupling between the switch input and the switch output. Ultra-high isolation can be achieved by adding a coupled transmission line to the semiconductor switch. The coupled transmission line introduces inductive coupling, which cancels at least a part of the capacitive coupling between the switch input and the switch output.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference under 37 CFR 1.57.

BACKGROUND

Field of the Invention

The present invention is generally in the field of semiconductors, andmore particularly, to semiconductor switches.

Description of the Related Art

In semiconductor switches, the isolation is limited by the capacitivecoupling between the switch input and the switch output. The isolationcan be improved by increasing the number of semiconductor devices inseries and by reducing the semiconductor device size. However, thisincreases the insertion loss.

SUMMARY

Ultra-high isolation in semiconductor switches can be achieved by addinga coupled transmission line to the semiconductor switch. The coupledtransmission line introduces inductive coupling, which cancels at leasta part of the capacitive coupling between the switch input and theswitch output.

According to a number of embodiment, the disclosure relates to aswitching circuit comprising a coupled transmission line including afirst transmission line and a second transmission line, and a pluralityof transistors forming a switch and configured to switch an input signalfrom a first port to a second port through the first transmission lineand to disconnect the first port from a third port, where the secondtransmission line induces an inductive signal which cancels at least aportion of a capacitive signal generated by the input signalcapacitively coupling through the switch to the third port.

In an embodiment, the plurality of transistors include a first and asecond transistor electrically connected in series and having a commonterminal, a first terminal, and a second terminal, where the commonterminal is electrically connected to the first port, the first terminalis electrically connected to the second port through the firsttransmission line, and the second terminal is electrically connected tothe third port through the second transmission line.

In another embodiment, the switching circuit further comprises a thirdtransistor electrically connected to the first terminal and a fourthtransistor electrically connected to the second terminal. In a furtherembodiment, the first, second, third and fourth transistors includefield-effect transistors (FETs). In a yet further embodiment, at leastone of the plurality of transistors includes four transistor deviceselectrically connected in series. In another embodiment, the first portis electrically connected to a radio frequency (RF) antenna, the secondport is configured to receive an RF receive signal, and the third portis configured to receive an RF transmit signal. In another embodiment,the switch includes a single pole double throw (SPDT) switch.

Certain embodiments relate to a method to improve isolation of aswitching circuit. The method comprises receiving a radio frequency (RF)signal at a first port in a switching circuit, switching the switchingcircuit so as to electrically connect the first port to a second port inthe switching circuit and to electrically disconnect the first port froma third port in the switching circuit, and conducting the RF signal fromthe first port to the second port through a first transmission line of acoupled transmission line.

In an embodiment, the method further comprises inducing an inductivesignal in a second transmission line of the coupled transmission lineapproximately equal in magnitude and approximately opposite in phasefrom a capacitive signal generated by capacitive coupling of the RFsignal through the switching circuit to the third port. In anotherembodiment, the inductive signal cancels at least a portion of thecapacitive signal to provide isolation improvement.

In an embodiment, the method further comprises generating a capacitivesignal by capacitive coupling of the RF signal through the switchingcircuit to the third port. In another embodiment, the method furthercomprises inducing an inductive signal in a second transmission line ofthe coupled transmission line, wherein the inductive signal cancels atleast a portion of the capacitive signal to provide isolationimprovement.

In a further embodiment, the switching circuit includes a single poledouble throw (SPDT) switch, where the SPDT switch includes a first and asecond transistor electrically connected in series and having a commonterminal, a first terminal, and a second terminal, such that the commonterminal is electrically connected to the first port, the first terminalis electrically connected to the second port through the firsttransmission line, and the second terminal is electrically connected tothe third port through the second transmission line.

According to a number of embodiments, the disclosure relates to aswitching circuit implemented in a semiconductor die. The switchingcircuit comprises a first and a second transistor electrically connectedin series and having a common terminal, a first terminal, and a secondterminal, and a coupled transmission line including a first transmissionline and a second transmission line, where the first terminal iselectrically connected to a first port through the first transmissionline, the second terminal is electrically connected to a second portthrough the second transmission line, and the common terminal iselectrically connected to a third port. In an embodiment, the switchingcircuit further comprises a third transistor electrically coupled to thefirst terminal and a fourth transistor electrically coupled to thesecond terminal.

Certain other embodiments relate to a switching module comprising aswitching circuit implemented in a first semiconductor die. Theswitching circuit includes a plurality of transistors and a coupledtransmission line and is configured to switch an input signal from afirst port to a second port through a first transmission line of thecoupled transmission line and to disconnect the input signal from athird port, and at least one of a prefilter circuit, a post filtercircuit, a power amplifier circuit, a switch circuit, a down convertercircuit, and a modulator circuit implemented in a second semiconductordie.

In an embodiment, a capacitive signal is generated by capacitivecoupling of the input signal through the switching circuit to the thirdport. In another embodiment, an inductive signal induced in a secondtransmission line of the coupled transmission line cancels at least aportion of the capacitive signal to provide better isolation.

According to other embodiment, the disclosure relates to a portabletransceiver comprising an antenna configured to receive a radiofrequency (RF) input signal and to transmit an RF output signal, atransmitter configured to provide the antenna with the RF output signal,a receiver configured to amplify the received RF input signal, and aswitch including a plurality of transistors and a coupled transmissionline and configured to electrically couple the antenna to thetransmitter through a first transmission line of the coupledtransmission line and electrically couple the antenna to the receiverthrough a second transmission line of the coupled transmission line.

In an embodiment, the switch is switched to electrically couple theantenna to one of the transmitter and the receiver and to electricallydisconnect the antenna from the other of the transmitter and thereceiver. In another embodiment, a signal induced in the coupledtransmission line cancels at least a portion of a signal generated bycapacitive coupling in the switch to improve isolation of the switch. Ina further embodiment, the switch includes an ultra-high isolation singlepole double throw (SPDT) switch.

In a further embodiment, the plurality of transistors include a firstand a second transistor electrically connected in series and having acommon terminal, a first terminal, and a second terminal, where thefirst terminal is electrically connected to a transmit port through thefirst transmission line, the second terminal is electrically connectedto a receive port through the second transmission line, and the commonterminal is electrically connected to an antenna port. In a yet furtherembodiment, the plurality of transistors further include a thirdtransistor electrically connected to the first terminal and a fourthtransistor electrically connected to the second terminal. In anotherembodiment, the first, second, third and fourth transistors includefield-effect transistors (FETs).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of a single pole double throw (SPDT) switchconfigured to switch a radio frequency (RF) signal, according to certainembodiments.

FIG. 2 is a layout schematic of the SPDT switch of FIG. 1, according tocertain embodiments.

FIG. 3 is a circuit diagram of a SPDT switch including inductivecoupling and configured to switch an RF signal, according to certainembodiments.

FIG. 4A is a layout schematic of a SPDT switch with a coupledtransmission line, according to one embodiment.

FIG. 4B is a layout schematic of a SPDT switch with a coupledtransmission line, according to another embodiment.

FIG. 5A is an exemplary graph illustrating insertion loss for SPDTswitches with and without coupled transmission lines, according tocertain embodiments.

FIG. 5B is an exemplary graph illustrating isolation for SPDT switcheswith and without coupled transmission lines, according to certainembodiments.

FIG. 6 is an exemplary pole-zero plot illustrating the couplingcomponents of a SPDT switch with a coupled transmission line, accordingto certain embodiments.

FIG. 7 is an exemplary graph illustrating isolation for embodiments ofSPDT switches with a coupled transmission line with differing gapsbetween the transmission lines, according to certain embodiments.

FIG. 8A is an exemplary graph illustrating insertion loss forembodiments of SPDT switches.

FIG. 8B is an exemplary graph illustrating isolation for embodiments ofSPDT switches.

FIG. 9 is an exemplary block diagram of a semiconductor die including anembodiment of a SPDT switching circuit, according to certainembodiments.

FIG. 10 is an exemplary block diagram of switching module including anembodiment of the semiconductor die of FIG. 9, according to certainembodiments.

FIG. 11 is an exemplary block diagram illustrating a simplified portabletransceiver including an embodiment of an ultra-high isolation SPDTswitch, according to certain embodiments.

DETAILED DESCRIPTION

The features of the systems and methods will now be described withreference to the drawings summarized above. Throughout the drawings,reference numbers are re-used to indicate correspondence betweenreferenced elements. The drawings, associated descriptions, and specificimplementation are provided to illustrate embodiments of the inventionsand not to limit the scope of the disclosure.

FIG. 1 is a circuit diagram of a single pole double throw (SPDT) switchor switching circuit 100 that can be used to switch radio frequency (RF)signals. For example, multiband GSM-based mobile cellular handsetsgenerally include a number of circuits for the transmit (TX) and receive(RX) of the different bands of the handset. To select between the TX andRX modes of the various RF bands, a switching circuit is usuallyemployed at the antenna of the handset. The function of the switchingcircuit is to electrically connect the antenna of the cellular handsetto the TX or RX circuit of the band that is in use at a given time, andto simultaneously isolate all other sections of the handset from theantenna.

The SPDT switch 100 comprises a first transistor 120, a secondtransistor 122, a third transistor 124, and a fourth transistor 126. Inthe illustrated embodiment, transistors 120,122, 124, and 126 comprisefield-effect transistors (FETs). In other embodiments, the transistorscomprise bipolar-junction transistors (BJT), heterojunction-bipolartransistors (HBT), gallium arsenide field effect transistors (GaAsFET),or other active devices.

The SPDT switch 100 further comprises a first port 102, a second port104, and a third port 106, which are shown terminated to ground throughtermination loads 112, 114, and 116, respectively. In an embodiment,termination loads 112, 114, 116 each comprise approximately 50 ohms. Inan embodiment, the first port 102 comprises an antenna port, the secondport comprises a transmit (TX) port, and the third port comprises areceive (RX) port. In another embodiment, the first port 102 comprisesan antenna port, the second port comprises a RX port, and the third portcomprises a TX port.

FETs 120 and 126 are shunted to ground and are thus referred to as ShuntFETs. FETs 122 and 124 are connected in series and thus referred to asSeries FETs. A source of FET 120 and a source of FET 126 electricallycouple to ground. A drain of FET 120 and a drain of FET 122 electricallycouple to port 104. A source of FET 122 and a drain of FET 124electrically couple to port 102. A source of FET 124 and a drain of FET126 electrically couple to port 106. Gates of each FET 120, 122, 124,126 electrically couple to control signals (not shown) to open and closethe FETs 120, 122, 124, 126 to control the operation of the switch 100.Based on the control signals (not shown), the switch 100 can beconfigured to switch the signal 128 between port 102 and port 104 orbetween port 102 and port 106. As illustrated in FIG. 1, the switch 100is configured to switch a signal 128 from port 102 to port 104 such thatport 104 is electrically connected to port 102 (ON) and port 106 isdisconnected from port 102 (OFF).

However, as illustrated by dashed line 130, at least a portion of thesignal 128 flows from port 102 to port 106 even though the switchbetween port 102 and port 106 is open or OFF. This is due to capacitivecoupling through the switch 100 between the port 102 and the port 106.Isolation can be defined as the magnitude of a signal coupled across anopen circuit. The isolation of the switch 100 is limited by thecross-coupling or capacitive coupling (C_(off)) between the input andthe output of the switch 100 and can be improved by reducing C_(off).Another measure of the performance of a circuit is insertion loss, whichis the loss of signal power when the switching circuit is closed or ON.

FIG. 2 is a layout schematic of a SPDT switch 200 comprising a first FET220, a second FET 222, a third FET 224, a fourth FET 226 and ports 102,104, 106. In an embodiment, the switch 200 comprises the circuit of theSPDT switch 100, where FETs 222, 224 comprise Series FETs and FETs 220,226 comprise Shunt FETs. In the illustrated embodiment of FIG. 2, eachFET 220, 222, 224, 226 comprises a plurality of transistors ortransistor devices connected in series, as is known to one of skill inthe art from the description herein. In an embodiment, the Series FETs222, 224 each comprise a 174×23μ×14 FET having a finger number of 174, aunit finger width of approximately 23 microns, and 14 transistor deviceselectrically coupled in series. In an embodiment, the Shunt FETs 220,226 each comprise a 54×11.1μ×14 FET having a finger number of 54, a unitfinger width of approximately 11.1 microns, and 14 transistor deviceselectrically coupled in series.

In some instances, the isolation of the switch 200 can be improved orincreased by increasing the number of transistors in series and byreducing the device size of each of the transistors in series. However,reducing the device size can also increase the insertion loss of theswitch 200.

In an embodiment, high isolation can be achieved by connecting the SPDTswitch 100, 200 to a coupled transmission line. In an embodiment, thecoupled transmission line functions as a mutual inductor. FIG. 3 is acircuit diagram of an embodiment of a SPDT switch 300 includinginductive coupling. The SPDT switch 300 comprises a first transistor320, a second transistor 322, a third transistor 324, and a fourthtransistor 326. In the illustrated embodiment, transistors 320, 322,324, and 326 comprise field-effect transistors (FETs). In otherembodiments, the transistors comprise bipolar-junction transistors(BJT), heterojunction-bipolar transistors (HBT), gallium arsenide fieldeffect transistors (GaAsFET), or other active devices.

The SPDT switch 300 further comprises a first port 302, a second port304, and a third port 306, which are shown as being terminated to groundthrough termination loads 312, 314, and 316, respectively. In anembodiment, the termination loads 312, 314, 316 each compriseapproximately 50 ohms. In an embodiment, the first port 302 electricallycouples to an RF antenna, the second port 304 comprises a TX port whichis electrically coupled to RF transmit circuitry, and the third port 306comprises an RX port which is electrically coupled to RF receivecircuitry. In another embodiment, the first port 302 electricallycouples to the RF antenna, the second port 304 comprises the RX port,and the third port 306 comprises the TX port.

The SPDT switch 300 further comprises a coupled transmission line 340including a first transmission line 342 and a second transmission line344. In certain embodiments, coupled transmission lines further comprisea ground, which can be a part of a backside metallization layer of asemiconductor die. In an embodiment, the first and second transmissionlines 342, 344 of the coupled transmission line 340 act as inductors.Mutual inductance occurs when the change in current in one inductorinduces a voltage in another nearby inductor.

FETs 320 and 326 (Shunt FETs) are shunted to ground and FETs 322 and 324are connected in series (Series FETs). A source of FET 320 and a sourceof FET 326 electrically couple to ground. A drain of FET 320 and a drainof FET 322 electrically couple to port 304 through the firsttransmission line 342. A source of FET 322 and a drain of FET 324electrically couple to port 302. A source of FET 324 and a drain of FET326 electrically couple to port 306 through the second transmission line344. Gates of each FET 320, 322, 324, 326 electrically couple to controlsignals (not shown) to open and close the FETs 320, 322, 324, 326 tocontrol the operation of the switch 300. Based on the control signals(not shown) the switch 300 can be configured to switch the signal 128between port 302 and port 304 or between port 302 and port 306. Asillustrated in FIG. 1, the switch 300 is configured to switch the signal128 from port 302 to port 304 such that port 304 is electricallyconnected to port 302 (ON) and port 306 is disconnected from port 302(OFF).

As illustrated by dashed line 330, at least a portion of the signal 128flows from port 302 to port 306 even though the switch 300 between port302 and port 306 is OFF. The capacitive signal 330 is due to capacitivecoupling (C_(off)) of the OFF FET 324 between the port 302 and the port306. In switch 300, the capacitive signal 330 flows from the port 302through the second transmission line 344 of the coupled transmissionline 340 to the port 306. An inductive signal 332 is induced by thesignal current via the coupled transmission line 340. The inductivesignal 332 cancels at least a portion of the capacitive signal 330 toprovide greater isolation for the switching circuit 300. In anembodiment, the switch 300 comprises an ultra-high isolation switch.

FIG. 4A is an embodiment of a layout schematic of a SPDT switch 400. Inan embodiment, the SPDT switch 400 comprises the circuit diagram of theSPDT switch 300. The switch 400 comprises a first FET 420, a second FET422, a third FET 424, and a fourth FET 426, where FETs 422, 424 compriseSeries FETs and the FETs 420, 426 comprise Shunt FETs. In an embodiment,the series FETs 422, 424 each comprise 14 transistor deviceselectrically coupled in series and the shunt FETs 420, 426 each comprise14 transistor devices electrically coupled in series. In an embodiment,the Series FETs 422, 424 each comprise a 174×23μ×14 FET having a fingernumber of 174, a unit finger width of approximately 23 microns, and 14transistor devices electrically coupled in series. In an embodiment, theShunt FETs 420, 426 each comprise a 54×11.1μ×14 FET having a fingernumber of 54, a unit finger width of approximately 11.1 microns, and 14transistor devices electrically coupled in series.

In other embodiments, the Series FETs 422, 424 and/or the Shunt FETs420, 426 comprise more than or less than 14 transistors in series. In anembodiment, the Series FETs 422, 424 comprise a finger number greaterthan 174. In an embodiment, the Series FETs 422, 424 comprise a fingernumber less than 174. In an embodiment, the Series FETs 422, 424comprise a unit finger width greater than approximately 23 microns. Inan embodiment, the Series FETs 422, 424 comprise a unit finger widthless than approximately 23 microns. In an embodiment, the Shunt FETs420, 426 comprise a finger number greater than 54. In an embodiment, theShunt FETs 420, 426 comprise a finger number less than 54. In anembodiment, the Shunt FETs 420, 426 comprise a unit finger width greaterthan approximately 11.1 microns. In an embodiment, the Shunt FETs 420,426 comprise a unit finger width less than approximately 11.1 microns.

The switch 400 further comprises a coupled transmission line 440comprising a first transmission line 442 and a second transmission line444. In an embodiment, the coupled transmission line 440 has a length ofapproximately 270 microns, a width of approximately 10 microns, and agap between the first transmission line 442 and the second transmissionline 444 of approximately 2 microns.

In other embodiments, the length of the coupled transmission line 440 isgreater than approximately 270 microns. In an embodiment, the length ofthe coupled transmission line 440 is less than approximately 270microns. In an embodiment, the width of the coupled transmission line440 is greater than approximately 10 microns. In an embodiment, thewidth of the coupled transmission line 440 is less than approximately 10microns. In an embodiment, the gap between the first transmission line442 and the second transmission line 444 is greater than approximately 2microns. In an embodiment, the gap between the first transmission line442 and the second transmission line 444 is less than approximately 2microns.

FIG. 4B is an embodiment of a layout schematic of a SPDT switch 450. Inan embodiment, the SPDT switch 450 comprises the circuit diagram of theswitch 300. The switch 450 comprises a first FET 470, a second FET 472,a third FET 474, and a fourth FET 476, where FETs 472, 474 compriseSeries FETs and the FETs 470, 476 comprise Shunt FETs. In an embodiment,the Series FETs 472, 474 each comprise four (4) transistor deviceselectrically coupled in series and the shunt FETs 470, 476 each comprise14 transistor devices electrically coupled in series.

In other embodiments, the Series FETs 472, 474 comprise more than orless than 4 transistors in series and the Shunt FETs 470 and 476comprise more than or less than 14 transistors in series.

The switch 450 further comprises a coupled transmission line 490comprising a first transmission line 492 and a second transmission line494. Each coupled transmission line 440, 490 has a length 446 and a gap448. The gap 448 comprises the space on the layout between theindividual transmission lines. For example in FIG. 4A, the gap 448comprises the space on the layout between the individual transmissionlines 442, 444 of the coupled transmission line 440. In another example,the gap 448 comprises the space on the layout between the individualtransmission lines 492, 494 of the coupled transmission line 490 in FIG.4B.

Insertion loss can be limited by the number of transistors in seriesthat comprise the FETs. On the other hand, greater numbers oftransistors in series leads to improved isolation. FIG. 4B illustrates areduced number of transistor devices in series for the Series FETs 472,474, which improves insertion loss for the switch 450 and the additionof the coupled transmission line 490 improves the isolation of theswitch 450. Thus, switch 450 has good insertion loss and isolationperformance and can use less layout area than switch 400.

In an embodiment, the coupled transmission line 440, 490 comprises astripline, a microstrip, a coplanar wave guide (CPW), or the like.

FIG. 5A is an exemplary graph 500 illustrating insertion loss versusfrequency for embodiments of SPDT switches with and without coupledtransmission lines. Insertion loss can be defined as the loss of signalpower for signals and is measured in dB, as indicated by the y-axis. Thex-axis indicates the frequency of the signal 128 in GHz. Plot 502represents the insertion loss for signals 128 switched by SPDT switchingcircuits 100, 200 without coupled transmission lines. Plot 504represents the insertion loss for signals 128 switched by SPDT switchingcircuits 300, 400, 450 including the coupled transmission line 340, 440,490, respectively.

For frequencies between approximately 1 GHz to approximately 6 GHz, theinsertion loss 502 is slightly better (higher) for switching circuits100, 200 without coupled transmission lines than the insertion loss 504for switching circuits 300, 400, 450 including coupled transmissionlines 340, 440, 490, respectively. For example, at approximately 2.0GHz, the insertion loss for switching circuits 100, 200 is approximately0.02 dB greater that for switching circuits 300, 400, 450.

FIG. 5B is an exemplary graph 550 illustrating isolation versusfrequency for embodiments of SPDT switches with and without coupledtransmission lines. Isolation can be defined as the magnitude of asignal coupled across an open circuit, and is measured in dB, asindicated by the y-axis. The x-axis indicates the frequency of thesignal 128 in GHz. Plot 552 represents the insertion loss for signals128 switched by SPDT switching circuits 100, 200 without a coupledtransmission line. Plot 554 represents the insertion loss for signals128 switched by SPDT switching circuits 300, 400, 450 including thecoupled transmission lines 340, 440, 490, respectively.

For frequencies between approximately 1 GHz to approximately 6 GHz, theisolation is much better (lower) for switching circuits 300, 400, 450including coupled transmission lines 340, 440, 490 than for switchingcircuits 100, 200 without coupled transmission lines. For example, atapproximately 2.0 GHz, the isolation for switching circuits 300, 400,450 is approximately 21 dB less than for switching circuits 100, 200.

FIG. 6 is an exemplary pole-zero plot 600 illustrating the amplitude andphase of coupling components of the signal 128 switched by an embodimentof the SPDT switch 300, 400, 450 with the coupled transmission line 340,440, 490, respectively, for signal frequencies between approximately 1.0GHz and approximately 3.0 GHz. The coupling components comprise acapacitive coupling component 602, an inductive coupling component 604,and a resultant coupling component 604.

In an embodiment, the capacitive coupling component 602 corresponds tothe signal 330 and the inductive coupling component 604 corresponds tothe signal 332. The capacitive coupling component 602 and the inductivecoupling component 604 are comparable in magnitude but approximatelyopposite in phase. The resultant coupling component 606 comprises thesum of the capacitive coupling component 602 and the inductive couplingcomponent 604. As illustrated in FIG. 6, the inductive couplingcomponent 604 induced by the addition of the coupled transmission line340, 440, 490 cancels at least a portion of the capacitive couplingcomponent 602. In an embodiment, at least one of the transmission linelength 446 and the transmission line gap 448 is varied to create theinductive coupling component 604 that is approximately equal inmagnitude to the capacitive coupling component 602 in order to minimizethe resultant component 606.

Thus, the resultant coupling component 606 is less than the capacitivecoupling component 602 and the inductive coupling component 604,resulting in improved isolation for the switches 300, 400, 450 over thatof the switches 100, 200. In an embodiment, the switches 300, 400, 450comprise ultra-high isolation switches.

FIG. 7 is an exemplary graph 700 illustrating the relationship betweenthe transmission line length 446, the transmission line gap 448, and theisolation of the switch 300, 400, 450 for the signal 128 atapproximately 1 GHz. The isolation is measured in dB and is indicated bythe y-axis. The x-axis indicates the length of the coupled transmissionline 340, 440, 490 and is measured in microns. Plot 702 is a plot of theisolation versus transmission line length 446 for an embodiment of theswitch 300, 400, 450 having the transmission line gap 448 ofapproximately 5 microns. Plot 704 is a plot of the isolation versustransmission line length 446 for an embodiment of the switch 300, 400,450 having the transmission line gap 448 of approximately 2 microns.

The best (minimum) isolation can be achieved by optimizing thetransmission line length 446 for a selected transmission line gap. Forthe embodiment of the switch 300, 400, 450 comprising the approximately5 micron transmission line gap, the best isolation occurs when thelength 446 of the coupled transmission line 340, 440, 490 isapproximately 262 microns. For the embodiment of the switch 300, 400,450 comprising the approximately 2 micron transmission line gap, thebest isolation occurs when the length 446 of the coupled transmissionline 340, 440, 490 is approximately 275 microns.

FIG. 8A is an exemplary graph 800 illustrating insertion loss forembodiments of the SPDT switch. The insertion loss is measured in dB andindicated on the y-axis. The x-axis indicates the frequency of thesignal 128 in GHz. Plot 802 illustrates the insertion loss for the SPDTswitch 450 comprising the coupled transmission line 490 and series FETs472, 474, where each series FET 472, 474 includes four transistordevices electrically coupled in series. Plot 804 illustrates theinsertion loss for the SPDT switch 200 without the coupled transmissionline and comprising the series FETs 222, 224, where each series FET 222,224 includes 14 transistor devices electrically coupled in series.

For example, when the signal 128 is approximately 2.1 GHz, the insertionloss of both switches 200, 450 is approximately −0.33 dB. For signals128 less than approximately 2.1 GHz to approximately 1.0 GHz, the switch450 shows better insertion loss performance and for signals 128 greaterthan approximately 2.1 GHz to approximately 3.0 GHz, the switch 200shows better insertion loss performance.

FIG. 8B is an exemplary graph 850 illustrating isolation for embodimentsof the SPDT switch. The isolation is measured in dB and is indicated onthe y-axis. The x-axis indicates the frequency of the signal 128 in GHz.Plot 852 illustrates the isolation for the SPDT switch 450 comprisingthe coupled transmission line 490 and series FETs 472, 474, where eachseries FET 472, 474 includes four transistor devices electricallycoupled in series. Plot 854 illustrates the isolation for the SPDTswitch 200 without the coupled transmission line and comprising theseries FETs 222, 224, where each series FET 222, 224 includes 14transistor devices electrically coupled in series.

As illustrated in FIG. 8B, the isolation performance of the switch 450(plot 852) is much better than the isolation performance of the switch200 (plot 854). For example, at approximately 1 GHz, the isolation ofthe switch 200 (plot 854) is approximately −43 dB, while the isolationof the switch 450 (plot 852) is approximately −83 dB.

Improvement in both insertion loss and isolation performance can beachieved by optimizing the number of series transistors comprising theSeries FETs, the transmission line length 446, and the transmission linegap 448.

FIG. 9 is an exemplary block diagram of a semiconductor die 900including a switching circuit 902. In one embodiment, the switchingcircuit 902 comprises the SPDT switch 300, 400, 450. In anotherembodiment, the switching circuit 902 comprises the SPDT switch 100,200. In a further embodiment, the switching circuit 902 comprises aswitch circuit including at least one pole, at least one throw, and atleast one coupled transmission line. In an embodiment, the semiconductordie 900 comprises a silicon (Si) die. In another embodiment, the die 900can comprise a gallium arsenide (GaAs) die, a pseudomorphic highelectron mobility transistor (pHEMT) die, or the like.

FIG. 10 is an exemplary block diagram of switching module 1000 includingthe semiconductor die 900 of FIG. 9. The module 1000 further includesconnectivity 1002 to provide signal interconnections, packaging 1004,such as for example, a package substrate, for packaging of thecircuitry, and other circuitry die 1006, such as, for exampleamplifiers, pre-filters, post filters modulators, demodulators, downconverters, and the like, as would be known to one of skill in the artof semiconductor fabrication in view of the disclosure herein.

FIG. 11 is an exemplary block diagram illustrating a simplified portabletransceiver 1100 including an embodiment of the very high isolation SPDTswitch 300, 400, 450 configured to switch, for example, a signal betweenthe antenna port and the RX and TX ports.

The portable transceiver 1100 includes a speaker 1102, a display 1104, akeyboard 1106, and a microphone 1108, all connected to a basebandsubsystem 1110. A power source 1142, which may be a direct current (DC)battery or other power source, is also connected to the basebandsubsystem 1110 to provide power to the portable transceiver 1100. In aparticular embodiment, portable transceiver 1100 can be, for example,but not limited to a portable telecommunication device, such as a mobilecellular-type telephone. The speaker 1102 and the display 1104 receivesignals from baseband subsystem 1110, as known to those skilled in theart. Similarly, the keyboard 1106 and the microphone 1108 supply signalsto the baseband subsystem 1110. The baseband subsystem 1110 includes amicroprocessor (μP) 1120, memory 1122, analog circuitry 1124, and adigital signal processor (DSP) 1126 in communication via bus 1128. Bus1128, although shown as a single bus, may be implemented using multiplebusses connected as necessary among the subsystems within the basebandsubsystem 1110. The baseband subsystem 1110 may also include one or moreof an application specific integrated circuit (ASIC) 1132 and a fieldprogrammable gate array (FPGA) 1130.

The microprocessor 1120 and memory 1122 provide the signal timing,processing, and storage functions for portable transceiver 1100. Theanalog circuitry 1124 provides the analog processing functions for thesignals within baseband subsystem 1110. The baseband subsystem 1110provides control signals to a transmitter 1150, a receiver 1170, a poweramplifier 1180, and a switching module 1190, for example.

It should be noted that, for simplicity, only the basic components ofthe portable transceiver 1100 are illustrated herein. The controlsignals provided by the baseband subsystem 1110 control the variouscomponents within the portable transceiver 1100. Further, the functionof the transmitter 1150 and the receiver 1170 may be integrated into atransceiver.

The baseband subsystem 1110 also includes an analog-to-digital converter(ADC) 1134 and digital-to-analog converters (DACs) 1136 and 1138. Inthis example, the DAC 1136 generates in-phase (I) and quadrature-phase(Q) signals 1140 that are applied to a modulator 1152. The ADC 1134, theDAC 1136, and the DAC 1138 also communicate with the microprocessor1120, the memory 1122, the analog circuitry 1124, and the DSP 1126 viabus 1128. The DAC 1136 converts the digital communication informationwithin baseband subsystem 1110 into an analog signal for transmission tothe modulator 1152 via connection 1140. Connection 1140, while shown astwo directed arrows, includes the information that is to be transmittedby the transmitter 1150 after conversion from the digital domain to theanalog domain.

The transmitter 1150 includes the modulator 1152, which modulates theanalog information on connection 1140 and provides a modulated signal toupconverter 1154. The upconverter 1154 transforms the modulated signalto an appropriate transmit frequency and provides the upconverted signalto the power amplifier 1180. The power amplifier 1180 amplifies thesignal to an appropriate power level for the system in which theportable transceiver 1100 is designed to operate.

Details of the modulator 1152 and the upconverter 1154 have beenomitted, as they will be understood by those skilled in the art. Forexample, the data on connection 1140 is generally formatted by thebaseband subsystem 1110 into in-phase (I) and quadrature (Q) components.The I and Q components may take different forms and be formatteddifferently depending upon the communication standard being employed.

The power amplifier 1180 supplies the amplified signal to a front-endmodule 1162. The front-end module 1162 comprises an antenna systeminterface that may include, for example, the switching module 1190comprising an embodiment of the switch 300, 400, 450 for switching asignal between the antenna port, the RX port, and the TX port, asdescribed herein to improve the isolation performance of the switch. Thetransmit signal is supplied from the front-end module 1162 to theantenna 1160.

In an embodiment, the front-end module 1162 comprises the switchingmodule 1190. In an embodiment, switching module 1190 comprises theswitching module 1000 including the semiconductor die 900. In theseembodiments, the switching circuit in the semiconductor die 900 is anembodiment of the switch 300, 400, 450.

A signal received by antenna 1160 will be directed from the front-endmodule 1162 to the receiver 1170. The receiver 1170 includes low noiseamplifier circuitry 1172, a downconverter 1174, a filter 1176, and ademodulator 1178.

If implemented using a direct conversion receiver (DCR), thedownconverter 1174 converts the amplified received signal from an RFlevel to a baseband level (DC), or a near-baseband level (approximately100 kHz). Alternatively, the amplified received RF signal may bedownconverted to an intermediate frequency (IF) signal, depending on theapplication. The downconverted signal is sent to the filter 1176. Thefilter 1176 comprises at least one filter stage to filter the receiveddownconverted signal as known in the art.

The filtered signal is sent from the filter 1176 to the demodulator1178. The demodulator 1178 recovers the transmitted analog informationand supplies a signal representing this information via connection 1186to the ADC 1134. The ADC 1134 converts these analog signals to a digitalsignal at baseband frequency and transfers the signal via bus 1128 tothe DSP 1126 for further processing.

Other Embodiments

While embodiments have been described with respect to a SPDT switch, thedisclosed systems and methods apply to any switch, such as, for example,SPST, DPST, and DPDT switches, switches with more than one pole,switches with more than one throw, and the like, as would be known toone of skill in the art in view of the disclosure herein.

While embodiments have been described with respect to the switchswitched so as to electrically connect port 102 to port 104 anddisconnect port 102 from port 106, the disclosed systems and methodsapply to the switch switched so as to electrically connect port 102 toport 106 and disconnect port 102 from port 104, as would be known to oneof skill in the art in view of the disclosure herein.

While embodiments have been described with respect to the signal 128flowing from port 102 to port 104, the disclosed systems and methodsapply to the signal 128 flowing from port 102 to port 106, from port 104to port 102, or from port 106 to port 102, as would be known to one ofskill in the art in view of the disclosure herein

In an embodiment, such as one needing narrow-band isolation, the switch300, 400, 450 can be laid out to optimize R_(on) and cancel out at leasta portion of the capacitive coupling 330.

In another embodiment, the switch 100, 200 could further comprise aninductor bridging the Series FETs 122, 124; and 222, 224, respectively.The inductor induces an inductive signal to cancel at least a portion ofthe capacitive signal 330 caused by capacitive coupling between an inputport of the switch 100, 200 and an inactive (OFF) output port of theswitch 100, 200. Such cross-biasing can improve the insertion loss,isolation, and bandwidth, and the inductor takes up less area on thesemiconductor die 900 than the coupled transmission line 340, 440, 490.

In a further embodiment, the switch 300, 400, 450 could further comprisean inductor bridging the Series FETs 322, 324; 422, 424; and 472, 474,respectively, as well as the coupled transmission line 340, 440, 490,respectively, to further improve the isolation of the switching circuit.

Terminology

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,” and thelike are to be construed in an inclusive sense, as opposed to anexclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to.” The words “coupled” or connected”, asgenerally used herein, refer to two or more elements that may be eitherdirectly connected, or connected by way of one or more intermediateelements. Additionally, the words “herein,” “above,” “below,” and wordsof similar import, when used in this application, shall refer to thisapplication as a whole and not to any particular portions of thisapplication. Where the context permits, words in the above DetailedDescription using the singular or plural number may also include theplural or singular number respectively. The word “or” in reference to alist of two or more items, that word covers all of the followinginterpretations of the word: any of the items in the list, all of theitems in the list, and any combination of the items in the list.

Moreover, conditional language used herein, such as, among others,“can,” “could,” “might,” “may,” “e.g.,” “for example,” “such as” and thelike, unless specifically stated otherwise, or otherwise understoodwithin the context as used, is generally intended to convey that certainembodiments include, while other embodiments do not include, certainfeatures, elements and/or states. Thus, such conditional language is notgenerally intended to imply that features, elements and/or states are inany way required for one or more embodiments or that one or moreembodiments necessarily include logic for deciding, with or withoutauthor input or prompting, whether these features, elements and/orstates are included or are to be performed in any particular embodiment.

The above detailed description of certain embodiments is not intended tobe exhaustive or to limit the invention to the precise form disclosedabove. While specific embodiments of, and examples for, the inventionare described above for illustrative purposes, various equivalentmodifications are possible within the scope of the invention, as thoseordinary skilled in the relevant art will recognize in view of thedisclosure herein.

For example, while processes or blocks are presented in a given order,alternative embodiments may perform routines having steps, or employsystems having blocks, in a different order, and some processes orblocks may be deleted, moved, added, subdivided, combined, and/ormodified. Each of these processes or blocks may be implemented in avariety of different ways. In addition, while processes or blocks are attimes shown as being performed in series, these processes or blocks mayinstead be performed in parallel, or may be performed at differenttimes.

The teachings of the invention provided herein can be applied to othersystems, not necessarily the systems described above. The elements andacts of the various embodiments described above can be combined toprovide further embodiments.

While certain embodiments of the inventions have been described, theseembodiments have been presented by way of example only, and are notintended to limit the scope of the disclosure. Indeed, the novel methodsand systems described herein may be embodied in a variety of otherforms; furthermore, various omissions, substitutions, and changes in theform of the methods and systems described herein may be made withoutdeparting from the spirit of the disclosure. The accompanying claims andtheir equivalents are intended to cover such forms or modifications aswould fall within the scope and spirit of the disclosure.

What is claimed is:
 1. A portable transceiver comprising: an antennaconfigured to receive a radio frequency input signal and to transmit aradio frequency output signal; a transmitter configured to provide theantenna with the radio frequency output signal; a receiver configured toamplify the received radio frequency input signal; and a switchincluding a plurality of transistors and a coupled transmission line,the switch configured to switch between a first state and a secondstate, the antenna electrically coupled to the transmitter through afirst transmission line of the coupled transmission line anddisconnected from the receiver and a second transmission line of thecoupled transmission line when the switch is in the first state, theantenna electrically coupled to the receiver through the secondtransmission line and disconnected from the transmitter and the firsttransmission line when the switch is in the second state.
 2. Theportable transceiver of claim 1 wherein the switch is switched toelectrically couple the antenna to one of the transmitter and thereceiver and to electrically disconnect the antenna from the other ofthe transmitter and the receiver.
 3. The portable transceiver of claim 2wherein a signal induced in the coupled transmission line cancels atleast a portion of a signal generated by capacitive coupling in theswitch to improve isolation of the switch.
 4. The portable transceiverof claim 1 wherein the switch includes an ultra-high isolation singlepole double throw switch.
 5. The portable transceiver of claim 1 whereinthe plurality of transistors includes a first and a second transistorelectrically connected in series and having a common terminal, a firstterminal, and a second terminal, the first terminal in communicationwith the transmitter through the first transmission line, the secondterminal in communication with the receiver through the secondtransmission line, and the common terminal in communication with theantenna.
 6. The portable transceiver of claim 5 wherein the plurality oftransistors further includes a third transistor in communication withthe first terminal and a fourth transistor in communication with thesecond terminal.
 7. The portable transceiver of claim 6 wherein thefirst, second, third, and fourth transistors include field-effecttransistors.
 8. The portable transceiver of claim 6 wherein the first,second, third, and fourth transistors include bipolar-junctiontransistors.
 9. The portable transceiver of claim 6 wherein the first,second, third, and fourth transistors include gallium arsenidefield-effect transistors.
 10. The portable transceiver of claim 1wherein at least one of the plurality of transistors includes fourtransistor devices electrically connected in series.
 11. A method toimprove signal isolation in a portable transceiver, the methodcomprising: receiving a radio frequency signal at a switching circuithaving a transmit state and a receive state; switching the switchingcircuit so as to electrically connect an antenna to a transmitterthrough a first transmission line of a coupled transmission line and toelectrically disconnect the antenna from a receiver and a secondtransmission line of the coupled transmission line when the switch is inthe transmit state, the radio frequency signal being conducted from thetransmitter to the antenna; and switching the switching circuit so as toelectrically connect the antenna to the receiver through the secondtransmission line and to electrically disconnect the antenna from thetransmitter and the first transmission line when the switch is in thereceive state, the radio frequency signal being conducted from theantenna to the receiver.
 12. The method of claim 11 further comprisingconducting the radio frequency signal from the transmitter to theantenna through the first transmission line when the switch is in thetransmit state.
 13. The method of claim 12 further comprising generatinga capacitive signal by capacitive coupling of the radio frequency signalthrough the switching circuit to the receiver.
 14. The method of claim13 further comprising inducing an inductive signal in the secondtransmission line of the coupled transmission line, the inductive signalcanceling at least a portion of the capacitive signal to provideisolation improvement.
 15. The method of claim 11 wherein the switchingcircuit includes a single pole double throw switch.
 16. The method ofclaim 11 wherein the switching circuit includes a first and a secondtransistor electrically connected in series and having a commonterminal, a first terminal, and a second terminal, the common terminalin communication with the antenna, the first terminal in communicationwith the transmitter through the first transmission line, and the secondterminal in communication with the receiver through the secondtransmission line.
 17. The method of claim 16 wherein at least one ofthe first and second, transistors includes four transistor deviceselectrically connected in series.
 18. The method of claim 16 wherein theswitching circuit further includes a third transistor in communicationwith the first terminal and a fourth transistor in communication withthe second terminal.
 19. The method of claim 18 wherein the first,second, third, and fourth transistors include field-effect transistors.20. The method of claim 18 wherein the first, second, third, and fourthtransistors include heterojunction-bipolar transistors.